Japanese Unexamined Patent Publication No. 2004-77281 discloses a navigation system which displays the positions of a host vehicle and its surrounding vehicle on an electronic map based on information on the position of the surrounding vehicle and the direction thereof which has been obtained from the surrounding vehicle by vehicle-to-vehicle communication and shows the travelling directions of the host vehicle and the surrounding vehicle with the points of arrows.
However, in the technique disclosed in Japanese Unexamined Patent Publication No. 2004-77281, when the navigation system is to be applied to a device which does not or cannot use an electronic map, the problem arises that it is difficult for the user thereof to recognize the relationship between the surrounding vehicle and the host vehicle of which the positions and travelling directions are displayed. The details are as follows.
If the positions of the host vehicle and the surrounding vehicle and the travelling directions thereof are displayed without displaying an electronic map, the user cannot recognize the relationship between the host vehicle and the surrounding vehicle such as the read/follow relationship therebetween or the relationship which will cross the host vehicle and the surrounding vehicle in the future based on the shapes of roads on an electronic map. As a result, the user has difficulty in recognizing the relationship between the host vehicle and the surrounding vehicle.
For example, a surrounding vehicle corresponding to a vehicle preceding a host vehicle on a curved road has the lead-follow relationship with the host vehicle. However, depending on the position thereof on the curved road, the travelling direction of the preceding vehicle may be greatly different from that of the host vehicle. In this case, if there is no display of an electronic map, the user has difficulty in recognizing that the host vehicle is following the foregoing preceding vehicle.